At present, most OLEDs (Organic Light-Emitting Diodes) are driven by direct current. Holes in an OLED enter into a light-emitting layer thereof from an anode, and electrons enter into the light-emitting layer from a cathode. The holes and the electrons recombine with each other in the light-emitting layer, and thus light can be emitted.
FIG. 1 is a schematic diagram of a circuit structure of pixels in an OLED display screen in the prior art. When a scanning line (Gate) corresponding to a row of pixels outputs a scanning signal, a transistor T1 is turned on. At this time, a driving signal output by a data line Data charges a capacitor C. A voltage of the capacitor C is taken as a gate voltage of a transistor T2. The on/off state of the transistor T2 can be controlled by the voltage of the capacitor C, and thus a magnitude of current flowing through the OLED can be controlled. When the OLED display screen operates, all of the pixels are kept continuously in the light-emitting state.
With the increase of the usage time of the OLED display screen, holes and electrons can accumulate on the interfaces of their respective transmission layers and light-emitting layers, thereby forming a built-in electric field in the OLED. This built-in electric field can increase a threshold voltage of the OLED, thus reducing its brightness. For OLED panels, due to the existence of built-in electric fields, an afterimage can easily appear on some static display areas thereof (e.g., TV station captions or advertisements displayed for a long time).